This invention relates to switch-mode circuitry and more particularly to controlling such switch-mode circuitry.
Semiconductor-based power electronic converters are often used to conform electrical power generated from various power sources to a fixed frequency (e.g., 60 Hz) phase-synchronized alternating current. Such power converters include inverters which convert (invert) DC to AC. These inverter circuits can be used in utility electrical power applications, as well as for adjustable speed drives (ASDs) for electric motors. A number of different design topologies are in use for the converters, which generally require an energy storage element to link the converters to the load. Unfortunately, in any inversion process, a portion of the generated power is wasted due primarily to the dissipation occurring within the large energy storage devices (e.g., inductors, capacitors) and within the semiconductor devices themselves. It is desired that any losses associated with the conversion and regulation of generated power be minimized.
The invention features a dual mode controller for controlling switching circuitry used for example in an inverter.
In a general aspect of the invention, the dual mode controller includes a voltage mode controller, a current mode controller, and a control circuit for operating the dual mode controller in a voltage mode or a current mode in response to an output signal of the switching circuitry.
A number of advantages are provided with a dual mode controller having both voltage mode and current mode controllers for operating in voltage and current modes, respectively. Operating in the voltage mode and current modes both have their attributes, each making them desirable for use in different circumstances. For example, during periods of operation in which the load is relatively xe2x80x9cwell-behavedxe2x80x9d (i.e., no large changes in load), voltage mode operation is preferable because the switching circuitry has less low frequency harmonics and generates lower system losses. However, the voltage mode of operation does not generally react well to large and fast changes in load, for example, due to transients at the load. In such circumstances, the dual mode controller uses its current mode controller. Although the current mode controller operates with less efficiency and generates more harmonics, its ability to provide a pulse width modulated waveform that can rapidly respond to transients while maintaining its frequency and phase characteristics is attractive. Furthermore, it is anticipated that for many applications the switching circuitry will be predominantly controlled by the relatively efficient voltage mode controller, and the current mode controller will be used only during those limited times that it is needed. Thus, smaller and less expensive components used for the switching circuitry can be used.
Embodiments of this aspect of the invention may include one or more of the following features.
The voltage mode controller and the current mode controller generate a first pulse width modulated (PWM) signal and a second pulse width modulated signal, respectively. The dual mode controller further includes a selector for receiving the first pulse width modulated signal and the second pulse width modulated signal and an output connected to the switching circuitry. The dual mode controller also includes sensing circuitry which generates an output signal from the switching circuitry and a control circuit. In response to the output signal from the sensing circuitry, the control circuit controls the selector to provide one of the first pulse width modulated signal and the second pulse width modulated signal to an input of the switching circuitry.
The voltage mode controller includes a processor including an input for receiving a DC voltage from a DC source and an output for providing a center-aligned first pulse width modulated signal. Among other advantages, operating the voltage mode controller using center-aligned pulse width modulation advantageously reduces the level of harmonics, thereby reducing noise and filter component dissipation.
The current mode controller includes a first comparator circuit having first and second inputs for receiving first and second reference signals, respectively, and a third input for receiving an output signal of the switching circuitry. The current mode controller also includes a logic circuit connected to the comparator circuit for providing the second pulse width generated waveform on the basis of the amplitude of the output signal of the switching circuitry relative to the amplitude of the first reference signal and second reference signal.
In operation, the control circuit of the dual mode controller is configured to control the selector to provide the second pulse width modulated signal to the input of the switching circuitry when the amplitude of the output signal of the switching circuitry is greater than the amplitude of the first reference signal or less than the amplitude of the second reference signal.
The control circuit also includes edge detection circuitry for examining edge transitions of the first pulse width modulated output signal and the second pulse width modulated output signal. In operation, the edge detection circuitry and processor of the voltage mode controller are configured to allow alignment of the edge transitions of pulses from the first pulse width modulated output signal with edge transitions of pulses from the second pulse width modulated output signal. Specifically, the edge detection circuitry calculates the time difference between edge transitions of pulses from the first pulse width modulated output signal with corresponding edge transitions of pulse from the second pulse width modulated output signal allowing the edge detection circuitry to adjust the hysteresis band (defined by the values of the first reference signal and the second reference signal), which can then be used to synchronize the pulses.
By ensuring that the edge transitions between the pulses of the first PWM output signal (from the voltage mode controller) align with corresponding edge transitions of pulse from the second PWM output signal (from the current mode controller), an effectively seamless transition between switching from current mode control to voltage mode control is provided. After transitioning back to the voltage mode, the control circuit resets the value of the first reference signal and the second reference signal to predetermined values for use by the voltage mode controller.
In another aspect of the invention, a dual mode controller is provided for controlling polyphase circuitry having a number of circuits operating with predetermined differential phase shifts relative to each other. In the polyphase arrangement, the dual mode controller includes a voltage mode controller, a current mode controller, and a control circuit that operates one of the voltage mode controller and current mode controller on the basis of at least one of a plurality of output signals from the switching circuits.
In embodiments of this aspect of the invention, the voltage mode controller and the current mode controller generate a first and a second plurality of pulse width modulated signals, respectively, for each of the circuits of the polyphase switching circuitry. A selector receives the first and second plurality of pulse width modulated signals and the second plurality of pulse width modulated signals. Sensing circuitry detects output signals from each of the circuits of the polyphase switching circuitry and generates a corresponding plurality of output signals. A control circuit, in response to the output signals from the sensing circuitry, controls the selector to provide one of the first plurality of pulse width modulated signals and the second plurality of pulse width modulated signals to an input of the switching circuitry. The multi-fold increase in efficiency offers a tremendous decrease in size of the components and cost of the overall system.
In still another aspect of the invention, a method for controlling switching circuitry includes operating in either a voltage mode or a current mode on the basis of an output signal of the switching circuitry.
In a related aspect of the invention, a method for controlling polyphase switching circuitry having switching circuits operating with predetermined differential phase shifts relative to each other. In this aspect, the method includes operating in the voltage mode or the current mode on the basis of an output signal from at least one of the switching circuits of the polyphase switching circuitry.
Embodiments of these aspects of the invention may include one or more of the following features. The voltage mode controller and current mode controller are used generate first and second pulse width modulated signals, respectively.
The output signal of the switching circuitry is sensed and a determination is made as to whether an amplitude level of the output signal is between a first amplitude level and a second amplitude level, which define a predetermined range. The switching circuitry is operated with the voltage mode controller when the amplitude level of the output signal is within the range. On the other hand the switching circuitry is operated with the current mode controller when the amplitude level of the output signal is outside the range. The determining step includes comparing the amplitude level of the output signal with the first amplitude level and the second amplitude level.
Operating in a voltage mode includes providing a first pulse width modulated waveform, preferably center-aligned, to the switching circuitry and operating in the current mode includes providing a second pulse width modulated waveform to the switching circuitry.
When operating in the current mode, the relative alignment of edge transitions of pulses from the first pulse width modulated waveform and the second pulse width modulated waveform is determined. Switching to the voltage mode occurs when the edge transitions of pulses from the first pulse width modulated waveform align with the second pulse width modulated waveform. In one embodiment, aligning the edge transitions of pulses from the first pulse width modulated waveform with edge transitions of pulses from the second pulse width modulated waveform includes adjusting the first amplitude level and the second amplitude level, which define the predetermined range.
After switching to the voltage mode from the current mode, resetting the first amplitude level and the second amplitude level to predetermined values. Resetting the first amplitude level and second amplitude level includes using a comparator circuit having inputs for receiving the predetermined values.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.